Technical Field
The present invention relates to a flying capacitor type voltage monitoring apparatus that uses a capacitor to monitor the voltage of a battery.
Related Art
A well-known battery monitoring apparatus based on related art, as disclosed in, for example, JP-B-3627922, monitors the voltage of a battery using a flying capacitor method. According to the flying capacitor method, the voltage of a battery is applied to a capacitor, and then the voltage applied to the capacitor is detected as a voltage of the battery.
JP-B-3627922 discloses a technique of detecting an on-failure (closing failure) of any of a plurality of input-side switches which are provided to turn on/off the connection of both terminals of a capacitor to both terminals of a battery. When an on-failure of a switch has occurred, the switch has been kept on and fails to be turned off. Specifically, JP-B-3627922 focuses on the matter that the voltage of the battery is applied to the capacitor when one of the input-side switches is turned on in a state where an on-failure has occurred in the input-side switches. Thus, the on-failure of the input-side switches can be detected on the basis of the voltage of the capacitor in turning on one of the input-side switches.
However, JP-B-3627922 just discloses detection of an on-failure in the input-side switches, but is silent about an on-failure in a plurality of output-side switches that turn on/off connection of both terminals of the capacitor to the voltage sensing terminals of the voltage detection circuit.
Similar to the detection of an on-failure in the input-side switches, an on-failure in the output-side switches may be detected on the basis of the detected voltage of the voltage detection circuit in turning on one of the output-side switches.
However, in turning on one of the output-side switches and turning off the rest of the output-side switches, the voltage sensing terminals of the voltage detection circuit, which correspond to the rest of the switches, will have high impedance. This may allow the voltage inputted to the voltage detection circuit to be unstable. Thus, voltage cannot be correctly detected in the voltage detection circuit. Therefore, an on-failure in the output-side switches cannot be detected by the voltage monitoring apparatus.